Calomel electrode vessel



Feb. s, 1929.. 1,700,796

D. s. HAKE CALOMEL ELECTRODE! IVES SEL Filed Nov. 2, 1926 .S ATTORNEYS 'W1' Patented Felt).` 5,A 1929.

U'Ni'rah sra'ras,

ricerca. paraat carica.

DONALD S. BAKE, F NIAGARA FALLS, NEW YORK, ASSIGNOR T0 AC'HESON GRAPHITE COMPANY, or NIAGARA FALLS, Naw YORK,

A coaroRA'rroN or Naw JERSEY.

cALoMEL nLEcTaoim VESSEL.

Application mea rnwemberv 2, 192s. serial No. 145,869.

In making electrometric titrations, a calomel electrode cell is employed, and is connected to 4the titrating cell by a contact tube. The material to be titrated is placed in the 5 titrating cell, and the change in potential of a pl atinumelectrode immersed in the solution is used to determine the end point of the titration.

Thus, in making titrations to determine in graphites, ferrousl the quantity 'of iron salts in a hydrochloric acid solution are oxi dized to ferric salts by standard potassium dichromate. The sample of graphite is first ashed in a Crucible furnace and the residue placed in a titrating cell and the iron dissolved in a given quantity of hydrochloric acid heated to incipient boiling. The iron is reduced with a few drops of stannous chlo` ride. The titrating cell is arrangedv in a 2o circuitincluding a potentiometer and a. calomelcell, and the circuit is completed from the titrating cell tothe calomel cell by means of a contact tube containing a solution of potassium chloride.

This contacttube must be flushed at intervals during the operation to remove air bubbles which break the electric circuit and also to remove solutions formed which diffuse withpotassium chloride solution in the contact tube.

In apparatus heretofore employed for this purpose the flushing solution of potassium chloride is delivered into the top of the calomel cell and the Contact tube communicates with the calomel cell ata point below the top. In `the lushing operation it frequently happens that some of the mercury salt in the bottom of the calomel cell is conveyed through the contact tube to the titrating cell with subsequent deleterious action on the latinum electrode in the titratingl cell. '1 This 1s shown by a falling 0H of the electromotive force. w l

An object of the present invention is to provide means for flushing the contact tube with potassium chloride solution without disturbing the mercury saltsin the bottom of the calomel vessel.

This mav Broadly, t e invention consists in the provision of means for preventting the incoming potassium chloride solution from Aiowlvng to the bottom of the calomel electrode vessel, or, in other words, means for retaining the main the calomel cell, and

be accomplished in severalvways. Y y

' which extends through the top of the titratl054 `terial in the bottom of the-calomel electrode vessel in a quiescent state while the potassium chloride 'solution is being delivered through the `top of the cell to the contact tube. A simple method of obtaining this result is to provide the contact tubewith a funnel shaped end and arrange the inlet or feed pipe for the potassium chloride solution in the end of the contact tube so that the flushing solution may be delivered directly' into the contact tube without disturbing the lmaterial in the calomel cell and at the same time the electric circuit from the titrating cell to the calomel cell is completed/through the liquidin the contact tube. In the accompanying drawings I have shown one form of calomel cell showing the improved contact tube. In this drawing, Fig. 1 is a' diagrammatic illustration of any e electrometric titration system showing the calomel cell in position, and Fig. 2 is a detail view of the calomel cell on an enlarged scale. Referring to the drawings, the lreference numeral 1 designates a titrating cell in which the titration is carriedout. The cell is providedy with an agitator or stirrer 2 mounted on aglass rod or shaft 3 which extends throug the top 4 and is provided with a drive pulley 5. During the titration, carbon dioxide is delivered to the titratixg cell from a suitable source through a pipe 6 which extends into a vessel 7 The vessel is provided with a stopper 8 having an outlet which is 'connected to the titrating cell by a pipe 9.

Standard potassium dlchromate is vplaced in a stoppered burette 10 and is delivered to the titrating cell through a pipe 11 having a valved outlet 12. The calomel cell 13 is arranged adjacent 4the titrating cell and mercury is arranged in the bottom of the calomel cell as indicated at 14. A layer of mercurous chloride or mercurous sulfate is. arranged above the mercury as indicated at 15, and the remainder of the cell isfilled with potassium chloride or potassium sulfate solution 16. This solution is delivered to the cell from a 100 reservoir 17 through a pipe 18 and the calomel cell is connected to the titrating cell by a contact tube 19, one endof which is arranged the other end of and the feed pipe 18 1s connected to a hollow stopper 21, the end of which is reduced as at, Il".

22 to loosely lit the flared end of the contactl tiometer is in turn connected to a galvanometer 26 by lead wire 27, and the opposite side of the galvanometer is provided' with a lead wire 28 connected to a platinum electrode 29 within l thel titrating cell. A voltmeter 30 may be connected to the wire 25 and the galvanometeras indicated in dotted lines.

In determining the amount of. iron in graphite, a sample of graphite is first ashed in a crucible furnace and theresidue dissolved in 50 c. c. of hydrochloric acid heated to incipient boiling and placed in the titrating cell 1. The apparatus used is essentially similar to that described by J. C.. Hosteller and H. S. Roberts in their paper on elec- Vtrometric titrations in the Journal of the' American Chemical Society (Vol. XLI, 1338, 1919). The hot solution is reduced with a few drops of-stannous chloride solution and the vtitrating cell introduced into thetitrating apparatus. A good-How of carbon dioxide -is maintained through the pipes 6 and 9 to prevent oxidation Ataking lplace. The agitator2 is placed in operation and the beam of the galvanometer balanced by means of Standard' potassium dichromate is .fed from the tube 10` by the valve 12 drop by drop and the beam ofthe potentiometer'` handwheel.

the galvanometerv is balanced by the hand vWheel of the potentiometer, the revolutions of'which are counted and which gradually increase per drop of potassium dichromate. The stannous chloride is first oxidized which point is indicated by a sharp increase in the number of revolutions.I Upon further addition of potassium dichromate va decrease to a minlmum results followed by an increase to a maximum and by a sharp decrease. A second `maximum is the end point'of the oxidation of the iron to the ferric state. E,

During titrating it is sometimes necessary to iush thev contact tube 19. Air bubbles which break the circuitaccumulate in this ltube and solutions which diluse, with the potassium chloride solution are somtimes formed. In the rdinaryconstruction of a calomel cell the' incoming potassium chloride /or potassiuml sulfate solution frequently causessome of the mercury salt in the bottom of t-he cell to be carriedinto'the contact tube trode 29 which is indicated by a falling olf of the E. M. F; The construction of a calomel cell, in which the flushing solution can be delivered into a contact tube VVWithout "disturbing the contents ofthe calomel cell, 'and at the vsame time maintaining the electric current between the calomel cell and thecontact tube,

is therefore a great advantage in the art. It` will be apparent that the construction shown permits the potassium chloride solution to flow into Contact tube 19 without disturbing the material in the bottom of the calomel cell. At the same time, the liquid in the tube isin communication with the liquid in the cell at all times and the circuit is thus complete ,through the vli uid to the mercur salt and mercuryin the ottom ofthe calomel cell and thence to the electrode 23.

While 'the use of the calomel electrode cell has been described in connection with'a titration to determine the quantity or iron in graphite,'such disclosure is nierely illustrative, and the improved cell is adapted to be used in any electrometric titration.

I claim:

1. A calomel electrode cell having an inlet at its upper end for the introductionot potassium chloride solution, a contacttube extending from said cell at a point below said inlet, and means to prevent the material in the bottom of said cell from being disturbed --when liquid' is being fed Itrom said inlet to said cont-act tube.

2. A calomel electrode cell having aninlet tube near its upper end 'for the introduction of potassium chloride solution and a contact tube extending from said cell at a. point below said inlet, the end of said inlet tube extending into said contact tube. c

3. 'Ai'ca'lomel electrode cell having aninlet tube near its upper end for the introduction of potassium chloride solution and a contact tube extending from said cell, -saidfcontact tube being oflarger diameter than said inlet tube and -surrounding the: end of said inlet tube. A y

In testimony whereof I afix my signature. 

